Catalyst stripping and apparatus therefor



Nov. 18, 1952 R. P. TRAINER ET AL CATALYST STRIPPING AND APPARATUS THEREFOR Filed Nov. 28, 1950 2 SHEETS--SHEET l Roacl'or Reaenerafor Z S'l'ripper' d l'eam l3 Air 5 7 Feed lol u n a! 0 lnvenl'ors'. Lawson E. Border Richard P. Trainer Nov. 18, 1952 R. P. TRAINER ET AL CATALYST STRIPPING AND APPARATUS THEREFOR Filed Nov. 28, 1950 2 SHEETSSHEET 2 Invenfors: Lawson E. Border i2 Th Patented Nov. 18, 1952 I I 2 I UNITED, STATES PATENT OFFICE "cA'rALYs'r s'rmrrmo AND APPARATUS THEREFOR Richard P. Trainer, Amityville, N. Y., and Lawson '15. Border, Westwood, N. J., assignors to Shell Development Company, Emeryville, CaliL, a corporation of Delaware Application November 28, 1950, Serial No. 197,958

3 Claims. (Cl. 34-57) improved method and apparatus in which efii- 5 tained by such methods has, however, been discient stripping may be accomplished in a pracappointingly small. Thus when stripping a spent tical manner in a short time. cracking catalyst by passing steam up through a In the catalytic conversion of hydrocarbons bed of the catalyst at a superficial velocity of and'related materials carried out with a regen- 0.8-feet/second substantially the same stripping erated powdered catalyst utilizing the fluid- 1 efficiency was obtained when operating at 850 F., ized catalyst technique, the powdered catalyst 950 F., and 1100 F. leaving the conversion zone contains occluded It has now been found why such methods have reactant material and is, furthermore, conhitherto failed to give the improvement hoped taminated with adsorbed products, polymers, for, and it ,has been found how to overcome the tars, and other organic materials of a relatively difliculty. It has been found that, aside 'from non-volatile nature. The direct passage of this the mentioned cracking, volatilization, and dispowder to the regeneration zone would not only placement phenomena, condensation reactions cause an appreciable waste of reactant and prodtake place which p d ce n -v latile and nonuct but would also greatly increase the difliculty .crackable polycyclic aromatic hydrocarbons in and cost of the subsequent regeneration treatthe catalyst. These condensation reactions take ment. Consequently, it is the practice to subplace at a'fairly rapid rate; this is evidenced by ject the powdered catalyst leaving the converthe substantial absence of olefins in the stripped sion zone to a treatment to remove the more pr d s ev n thou h large amounts of olefins are easily removable contaminants before passing present in the stripping feed. The Stripping the powder to the regeneration zone. This op- 5 eificiency can be improved and the advantages of eration, generally referred-to as stripping, conhigher tempe r pp g can be obtained if Sists of removing t more easily vam athese condensation reactions are prevented from terials by passing a stripping gas, e. g., steam, taking Place to y S bstantial extent. through the powder. By exhaustive treatment In broad gen ral Out ne h stripping of Such of the spent catalyst with steam, e. g., 900 F., catalyst is effected according to the present init is possible to remove combustible material up l by firs p y he e Sp ca to a certain point which may be considered the pow rto a ig er temperature while out of conultimate stripping. In practice, however, such tact Withthestripping um to initiate crackexhaustive treatment would be prohibitive as s and effect substantial volatilization of adwell as detrimental for other reasons and is sorbed t r f w d y a ap d removal of never applied. The stripping in commercial opthe interstitial vap rs, and finally stripping for eration using conventional stripping methods a l r p riod of time in a dense Ph se under is usually of the order 01' -60% eflicient on the onditi ns to allow the cracking and vaporization, above basis, to proceed to the fullest extent in the substantial The importanceof the stripping efficiency has 40 absence of pped vapors. h Operation may been recognized and many attempts have been be conveniently carried out in a stripper of the made to improve the efiiciency in a practical design illustrated in the accompanying drawings manner, i. e., without resorting to excessive wherein Figure I is a diagrammatic illustration amounts of steam and excessively large and cost- Of a fluidized catalyst catalytic c kin P an 1y apparatus. While minor improveme ts'have Provided wi h t e impr v d pper design; been obtained y these means in some a no ure II is a sectional elevation showing the internal substantial improvement has been achieved. n m t f on f r f h stripper; Figures This i d in pari; t th l of fundamental III and IV are sections through the respective knowledge of the chemistry, physics and meplanes of Figure II. Figure V is a sectional elechanics of stripping of such powders. It is Vetlon f a modified mixing ch m er which may known, however, that the stripping step is efiecbe used in place of the chamber M of Figure L tive in at least three ways which are: (1) inter- The p n in p r s in h r s bear the stitial vapors are largely removed, (2) some rela- Same reference mbers. A 'tively non-volatile adsorbed materials are vapor- .Referring o he r w n Fi ure I, a typical ized and removed and (3) some less volatile mafl dized catalyst catalytic cracking p1an proterials are decomposedinto more volatile products vided with the improved stripp n arrangement and are removed. On the basis of this knowlcomprises Q a re n r d a edge 11; would Seem t t t stripping efficiency separate stripper 3. For clearness, the reactor could be improved by stripping at a higher temand regenera'tor are shown spread out and the 0 stripper is shown much enlarged. Regenerated perature. Various methods for increasing the temperature have been suggested such, for example, as to add hot regenerated catalyst to the stripping zone and some improvement has been realized by such methods. The improvement obcatalyst is withdrawn 5. The hot regenerated catalyst is picked up tinuously withdrawn from. the reactor via line I at a rate controlled by slide valve 8 and passed to the stripper. A stream of hot regenerated catalyst it likewise withdrawn from the regenerator via line 9 at a rate controlled by valve l and is passed by gravity to the stripper. The stripped catalyst leaves the'stripper via line H at a rate controlled by slide valve l2, and is picked up by stream of regeneration gas and transported via line is to the regenerator.

Referring to Figure II the spent catalyst enters the stripper 3 near the top via line I at substantially the temperature prevailing in the reactor, e. g., 800-1000 F. The hot regenerated catalyst enters the stripper 3 also near the top via line 9. This regenerated catalyst is at a temperature above that of the spent catalyst, e. g., 1000-1300 F. 1 The two streams of catalysts enter a small mixing chamber II which in the case illustrated is located within the stripper shell and consists of a dome-shaped vessel open at its lower end. Directly below the mixing chamber and in close proximity thereto is abaflle member IS. The

baifle and mixing chamber are so arranged and constructed that catalyst entering the mixing chamber may be somewhat held up but still allowed to discharge through the space between the members. The spent catalyst and hot regenerated catalyst are, therefore, caused to come into intimate contact for a short time suflicient to allow the two streams oi. catalyst to come to substantially the same temperature. In the case illustrated the mixing is effected without substantial contact with the stripping gas. The hot mixture of catalyst and liberated vapors issuing from the mixing chamber through the described space above the baflle is distributed and caused to fall (shower) for a short distance countercurrent to uprising stripping vapors, e. g. steam, which are introduced near the bottom of the stripper via line It. Disk and doughnut bailies l1 and iii are preferably provided to insure good contact of the descending rain of catalyst with the uprising stripping medium. Such baflles may be horizontal or inclined as illustrated. The described disperse phase stripping at'this point is important. However, it. is totally unnecessary and, in fact, undersirable that this disperse phase stripping consume any appreciable amountoi time. Since the contact time 01 the catalyst in the disperse phase is small this section of the stripper is not large and in no way compares with the large chambers hitherto provided when affecting the stripping entirely in the disperse phase. In this section 01' the stripper it is merely desired to displace as rapidly as possible the cracked and vaporized material between the catalyst particles and this may be accomplished with a very short contact time. Alter passing through the short disperse phase zone of the stripper the catalyst is allowed to collect into a substantial fluidized bed where it is further stripped in the so-called dense phase. The contact time of the catalyst in the dense phase ex, isting in the lower half of the stripper is much greater than in the mixing zone and disperse phase zone and is preferably as longfas can be economically justifled. For this reason it is desirable to maintain the level of the fluidized bed from the regenerator via standpipe 4 at a ratecontrolled by a slide valve 'and transported to the reactor by the feed via line B. Spent and contaminated catalyst is conshort dispersed phase contact in the zone immediate v above the bed. In order to improve the emciency oi the stripping in the dense phase section 0! the strippr: this section is preferably provided with vertical bailies is which divide this section into a number oi long vertical cells. stripping gas, e. g., steam, is preferably separately injected by suitable nozzles into each of the cells, as seen in Figure IV. The stripping gas, aiter'passing through the dense catalyst bed and the disperse catalyst phase, is flnally discharged via line 20 at the top. This stream may be passed to a conventional apparatus (not shown) to recover the stripped products or it may be passed to the top oi. the reactor in which case the stripped products are combined with the cracked given amount of the regenerated catalyst than it would it the spent catalyst and hot regenerated catalysts were simultaneously introduced into the fluidized bed. By excluding any substantial amount of the steam from the mixing zone*the entire available sensible heat is used to heat the spent catalyst and promote rapid vaporization and cracking of the constituents which tendto condense to polycyclic aromatics which resist cracking and remain in the catalyst. When the hot regenerated catalyst is supplied directly to the fluid bed being stripped the stripping steam absorbs a large amount of the sensible heat thus tending to lower the temperature'oi the bed; in order to obtain the desired temperature increase it is then necessary to circulate a larger quantity of the hot regenerated catalyst and this, in turn, lowers the contact time ot'the catalyst in the dense phase. In the described method these shortcomings .are avoided.

In the described method the vapors and cracked products .are quickly displaced by stripping medium in the short disperse phase contact afforded above the main catalyst bed. These materials are, therefore, quickly removed from the catalyst and prevented from entering into condensation reactions which tend to flx the carbonaceous matter in the catalyst.

In the lower section of the stripping zone, where the catalyst remains for a more extended period of time, the cracking of remaining absorbed material is given time to come to substantial completion. Since the main part of the occluded material is previously removed durin the short disperse phase contact the partial pressure of such products in the steam in the dense phase is negligible and this further helps to prevent condensation to non-volatile and noncrackable product's.

In the apparatus illustrated and described, the mixing of the contaminated catalyst and the hotter cataly t is effected in the dome-shaped vessel which has a diameter less than that of the stripper shell and is supported in the axis of the shell in the upper half. A sumcient space is allowed within the stripper above the mixing vessel in order to provide a quiescent upper zone (socalled disengaging zone). This apparatus may be modified'without departing Irom the principles described. Qne advantageous modification is illustrated in Figure 5. Here the mixing chamber, designated Ha, is inverted. The bottom is perforated. The perforations are small and suillcient to pass only a part 01' the powder introduced into the chamber by lines I and 9. In operation the cup-shaped chamber is filled and the powder overflows the upper lip into the dispersed phase section of the stripper. This design has the advantage that it is more flexible, i. e., a greater range of fiow rates may be applied. The perforations'are necessary in this "design to allow the chamber to drain when the operation is stopped. The operation cannot be started if the chamber is full of powder.

Emample In the catalytic cracking of gas oil the spent catalyst leaving the reactor contains about 1.95% combustible material and is at a temperature 01' 955' F. The catalyst is passed to the mixing zone where it is commingled with the regenerated catalyst having a temperature of about 1120" F. The ratio of fresh catalyst to regenerated catalyst continuously introduced into the mixing zone is about 23:1, The temperature in the mixing zone is about 1002 F. and the contact time is about three seconds. This hot mixture is allowed to fall from the mixing zone as a spray down through'the uprising stripping steam to the fluid bed, the contact time being 01' the order of five seconds. The hold-up of catalyst in the lower bed allows a contact time of thirty seconds. The amount of steam introduced into the bottom of the stripper is about three pounds per 1000 pounds catalyst. The loadin of the stripper is or the order of 520 pounds catalyst per minute per square foot of cross-section.

In this operation, the efllciency is substantially as good using only three pounds of steam as it is when using the larger amounts applied in conventional practice, e. g., six pounds. Also, the' total contact time of the catalyst with the steam is less than with conventional operation. This not only saves steam but is important since the contact of the catalyst with steam in the strip- .ping operation is the chief cause ofthe usual decline in the activity of the catalyst. Under proper conditions the short contact in the mixing zone and in the disperse phase (e. g., in total about eight seconds) has been determined to be equivalent in the stripping operation to about forty seconds stripping in the dense phase. Further contact in the disperse phase effects very little, it any, additional stripping and is undesirable since it utilizes space that can be more advantageously utilized for dense phase stripping. Thus, the approximatathirty seconds contact time afforded in the dense phase to complete the cracking and stripping brings the total contact time up to about e. g., 38 seconds, whereas in order to obtain an equivalent stripping in either the disperse phase or the dense phase a contact time of the order of 150 seconds would be required. This would require a larger stripping vessel for conventional dense phase stripping and a very much larger and more costly vessel for disperse phase stripping.

We claim as our invention: 1. An apparatus for the stripping of finely divided powder contaminated with volatilizable material which comprises in combination a vessel comprising a vertically disposed substantially 6 cylindrical shell having bottom and top closures, a lower conduit for the discharge of stripped powder, an upper conduit for the discharges: stripping vapors, vertical bailies dividing the lower section of said vessel into cells, means near the bottom of said shell for injecting stripping gases into able contaminants from powders which comprises in combination a vessel provided with top and bottom closures, an outlet near the top of said vessel for the discharge of gases, an outlet near the bottom of said vessel for the discharge of stripped powder, a dome-shaped mixing chamber open at the bottom supported within the up r half of said vessel, said 'mixing chamber having a diameter less than the internal diameter of the said vessel and being supported sufilciently below the top of the vessel to provide a settling space, a plate member supported below the said domeshaped mixing chamber at a distance to create a restricted ring-shaped passage for the eiiluent from said mixing chamber, separate conduits for the introduction of two streams of powder passing through the wall of said vessel into said mixing chamber and means for introducing a stripping gas near the bottom of said vessel below the said mixing chamber.

3. An apparatus for the stripping of volatilizable contaminants i'rom powders which comprises in combination a substantially cylindrical vessel having top and bottom closures, an outlet near the top of said vessel for the discharge of gases, an outlet near the bottom of said vessel for the discharge of stripped powder, a mixing chamber open at the top and with perforated bottom supported within the upper half of said vessel, said mixing chamber having a diameter less than the internal diameter of said vessel and supported within the upper half of: said vessel sumciently below the top to provide a settling space; disk and doughnut battles in said shell below said mixing chamber, vertical bailles dividing the lower section of said vessel into cells. means near the bottom of said shell for injecting stripping gas into said cells, and separate conduits for the introduction or two streams of powder passing through the wall of said vessel into said mixing chamber.

RICHARD P. TRAINER. LAWSON E. BORDER.

REFERENCES crrun file of this patent:

UNITED STATES PATENTS The following references are of record in th 

1. AN APPARATUS FOR THE STRIPPING OF FINELY DIVIDED POWDER CONTAMINATED WITH VOLATILIZABLE MATERIAL WHICH COMPRISES IN COMBINITATION A VESSEL COMPRISING A VERTICALLY DISPOSED SUBSTANTIALLY CYLINDRICAL SHELL HAVING BOTTOM AND TOP CLOSURES, A LOWER CONDUIT FOR THE DISCHARGE OF STRIPPED POWDER, AN UPPER CONDUIT FOR THE DISCHARGE OF STRIPPING VAPORS, VERTICAL BAFFLES DIVIDING THE LOWER SECTION OF SAID VESSEL INTO CELLS, MEANS NEAR THE BOTTOM OF SAID SHELL FOR INJECTING STRIPPING GASES INTO SAID CELLS, DISK AND DOUGHNUT BAFFLES IN SAID SHELL ABOVE SAID VERTICAL BAFFLES, A MIXING VESSEL WITHIN SAID VESSEL ABOVE SAID DISK AND DOUGHNUT BAFFLES AND BELOW SAID UPPER CONDUIT, SAID MIXING VESSEL HAVING SEPARATE INLET CONDUITS FOR TWO STREAMS OF POWDER, AND MEANS FOR DISTRIBUTING POWDER FROM SAID MIXING VESSEL OVER SAID DISK AND DOUGHNUT BAFFLES. 